The present invention relates to a method and apparatus for measuring the diameter of a silicon single crystal and more particularly to a silicon single crystal diameter measuring method and apparatus whereby during the continuous manufacture of a silicon single crystal while rotating it relative to a crucible the diameter of the pulled single crystal is measured during its pulling.
Referring to FIG. 2 of the accompanying drawings, there is illustrated a schematic diagram, showing a single crystal manufacturing apparatus utilizing the Czochralski method which is well known as a manufacturing method of single crystals of such semiconductor as silicon. It is to be noted that Czochralski method is widely known as a CZ method and also it is generally called as a crystal pulling method.
In the Figure, during the manufacture of a silicon single crystal, contained in a crucible 2 is molten silicon 3 which is heated and melted by a heater 4 so that while rotating a silicon single crystal 1 in a direction opposite to the direction of rotation of the crucible 2 by a turning mechanism which is not shown, the silicon single crystal 1 is gradually pulled from the molten silicon 3 by a pulling apparatus 7 and the crystal is grown in the interfacial region between the molten silicon 3 and the silicon single crystal 1. This silicon single crystal 1 is grown from a seed crystal 1a by crystal growth and the seed crystal 1a is supported by a seed crystal holder 6 connected to the pulling apparatus 7. In the discussion to follow, the silicon single crystal 1 under growth is referred to as a pulled single crystal. Also, the pulling apparatus 7 includes a mechanism for vertically moving the silicon single crystal 1 and a mechanism for rotating the crystal 1 and it is composed of a motor controller 8, a pull motor 9, etc. Thus, it is a well known apparatus and any detailed explanation of its construction will be omitted. The crucible 2 is supported by a lifting mechanism (not shown) in addition to the previously mentioned turning mechanism and it is designed so that even if a crystal is grown, for example, the liquid level is prevented from lowering but maintained constant by the lifting mechanism and the temperature distribution in the vicinity of the liquid surface is not varied.
The pulled single crystal 1 manufactured by the CZ method is later finished into a silicon single crystal ingot of a cylindrical shape and it is thus required that the crystal 1 is pulled with substantially the uniform diameter throughout the whole body portion. For this purpose, the diameter of the pulled single crystal is directly measured during its pulling by the optical means as a video measure 5 and it is pulled while adjusting the pull rate so as to maintain the diameter at the desired value. In this case, the optical means is attached to the crystal pulling apparatus and therefore the fusion ring appearing at the boundary of the pulled single crystal 1 and the liquid surface is measured obliquely from above by a single measuring line, thereby directly measuring the diameter of the pulled single crystal 1.
With the conventional silicon single crystal diameter measuring method and apparatus described, due to the fact that the diameter measuring optical means is attached to the silicon single crystal manufacturing apparatus and the fusion ring is measured obliquely from above with a single measuring line low-frequency noise is superimposed on the resulting measured diameter value under the effects of the rotation of the pulled single crystal and the rotation of the crucible. The superimposed noise increases the error of the measured value. Also, as shown in the schematic diagram of FIG. 3, the pulled single crystal 1 is not formed into a complete round shape due to the effect of crystal habit lines 13 so that when the crystal 1 is pulled while rotating it, if, for example, the diameter in an A direction is measured at a certain timing of a sampling measurement and the diameter in a B direction is measured at another timing, even if there is no change of the diameter with respect to the A direction, a change is caused in the diameter in terms of measurement. In addition, it is unavoidable that high-frequency noise is superimposed on the measured value due to an electrical effect. As a result, the occurrence of these factors causes an increase in variations of the measured diameter value of the pulled single crystal and the measured diameter value becomes unstable and unreliable.
For instance, where the data of such unreliable measured diameter value is used in the diameter control, the pull rate is varied so as to maintain uniform the diameter of the pulled single crystal. However, there is a disadvantage that not only this results in a meaningless control operation if there is in fact no variation in the diameter of the pulled single crystal but also the execution of a control on the basis of such data results in the execution of an erroneous control.